A317394 Positive integers that have exactly four representations of the form 1 + p1 * (1 + p2* ... * (1 + p_j)...), where [p1, ..., p_j] is a (possibly empty) list of distinct primes.

211, 261, 421, 426, 441, 484, 535, 540, 591, 621, 634, 667, 683, 691, 715, 726, 732, 761, 771, 776, 778, 794, 818, 853, 862, 871, 925, 970, 979, 987, 989, 1011, 1021, 1023, 1038, 1074, 1086, 1105, 1114, 1141, 1171, 1176, 1184, 1190, 1197, 1222, 1261, 1266

Offset

1,1

Links

Alois P. Heinz, Table of n, a(n) for n = 1..20000

Formula

A317241(a(n)) = 4.

Maple

b:= proc(n, s) option remember; local p, r; if n=1 then 1 else r:=0;
      for p in numtheory[factorset](n-1) minus s while r<5
        do r:= r+b((n-1)/p, s union {p}) od; `if`(r<5, r, 5)
      fi
    end:
a:= proc(n) option remember; local k; for k from
     `if`(n=1, 1, 1+a(n-1)) while b(k, {})<>4 do od; k
    end:
seq(a(n), n=1..100);

Crossrefs

Column k=4 of A317390.

Cf. A317241.

Sequence in context: A087833 A240918 A346948 * A096706 A001583 A308790

Adjacent sequences: A317391 A317392 A317393 * A317395 A317396 A317397

Keyword

nonn

Author

Alois P. Heinz, Jul 27 2018

Status

approved